European Patent EP 0 613 728 discloses a dispensing device for dispensing a foam, which dispensing device comprises a liquid container for holding the liquid that is to be dispensed and a dispenser assembly with two piston pumps which are positioned concentrically with respect to one another. The inner suction pump is used to pump a liquid, while the outer suction pump is used to pump air. The pumped air and liquid are mixed with one another in a mixing chamber, and a foam is formed while the mixture of air and liquid is passing through two porous elements; this foam is then dispensed via the foam dispenser opening.
One drawback of the known dispensing device is that the guidance between the cylinder and the piston of the piston pump can deteriorate over the course of time, leading to reduced piston pump function. Reduced guidance of this type may occur in particular in the case of an air pump.